The present invention relates to cellular mobile telecommunication systems. More particularly, the present invention relates to cellular mobile telecommunication systems that provide intelligent network (IN) services.
A typical cellular mobile telecommunication system comprises a plurality of geographic regions called cells. For example, the cellular mobile telecommunication system 100 depicted in FIG. 1 includes ten cells C1-C10. The cells are generally grouped into larger geographic regions called location areas (LAs). For illustrative purposes, cells C1-C10 are grouped into two such areas, LA1 and LA2, wherein LA1 includes cells C1-C5 and LA2 includes cells C6-C10.
Each cell contains at least one base station transceiver (BST), e.g., BST B1-B10, and each location area contains one or more mobile switching centers (MSCs), e.g., MSC1 and MSC2. Typically, each MSC is connected to several BSTs within the corresponding location area. A BST e.g., B1, communicates directly with the mobile units located in the corresponding cell, e.g., M1 and M2. The primary function of a MSC, however, is to execute the switching requirements necessary to properly route calls between a mobile unit located in one cell (e.g., M1) and a mobile unit located in another cell (e.g., M3). In addition, a MSC may be connected to a public switching telephone network (PSTN). Therefore, MSCs also facilitate the routing of calls between a mobile unit and a fixed telephone terminal connected to the PSTN.
Each mobile unit is associated with a particular "home" LA. Accordingly, the one or more MSCs servicing the "home" area will be responsible for handling the switching and routing of calls to and from each of these associated mobile units, so long as the mobile units are physically located in the "home" LA. If, however, a mobile unit travels into a second LA, the one or more MSCs servicing the second LA will become responsible for providing the switching and call routing requirements for the mobile unit. When a mobile unit enters a LA other than its "home" LA, the mobile unit is said to be "roaming."
There are a number of cellular system components used in providing a mobile unit with the capability of transmitting and receiving communications while roaming. Referring now to FIG. 2, one such additional system component is the home location register (HLR) 205. The HLR 205 is essentially a database associated with one or more MSCs in a given LA. The HLR 205 maintains a user record for each of a number of mobile units associated with the corresponding area; these mobile units are said to be assigned to the HLR 205. Each record contains, among other things, an identification code for the corresponding mobile unit, information regarding the type of service associated with that mobile unit, and information defining the current location of the mobile unit. Consequently, when a mobile unit roams into a second LA (i.e., a LA other than its "home" LA), the record for that mobile unit stored in the HLR 205 will be updated to reflect the mobile units new location, so that incoming calls can be properly forwarded to the mobile unit in the second LA.
Another system component that is used in providing a mobile unit with the capability to transmit and receive calls while roaming is the visiting location register (VLR) 210. The VLR 210 is also a database, and it is typically associated with an MSC, e.g., MSC 207. Unlike the HLR 205, the VLR 210 maintains a user record for each visiting mobile unit, for example mobile unit 215 (i.e., those mobile units currently located in the corresponding LA, though permanently assigned to a HLR located in another LA). When a mobile unit, for example mobile unit 215, roams into the LA, a record identifying that mobile unit will be established in the VLR 210. When the mobile unit 215 leaves the LA, the record in the VLR 210 is deleted.
In addition to basic cellular service, many cellular systems also provide IN services, which may include the ability to place originating IN calls. For example, an originating IN call might involve placing a call to a fixed telephone terminal by dialing only a four digit extension rather than the entire seven or ten digit phone number. Those skilled in the art will recognize that this service is often referred to as a private numbering plan.
As illustrated in FIG. 3, an additional system component, referred to as a service control point (SCP) 305, is needed to provide IN services. More particularly, the SCP 305 maintains the specific call routing instructions needed by the MSC 310 to properly route an IN service call for an IN subscriber assigned to HLR 315. In FIG. 3, MSC 310 is said to be an IN capable MSC.
However, not all MSCs in a cellular system are IN capable (i.e., capable of receiving and executing the IN call routing instructions maintained by the SCP). This is most troublesome for IN subscribers when they roam into areas that are serviced by non-IN capable MSCs. When this does occur, the IN subscriber is unable to place an originating IN service call. Therefore, a need exists to provide IN subscribers with a way to access their IN services even when the IN subscriber (i.e., the mobile unit) roams into an area serviced by a non-IN capable MSC.